1. Field of the Invention
The present invention relates to the field of transport technology, in particular in the area of post press processing. It relates to a method for operating a transport device and a transport device for implementing the method.
2. Discussion of Related Art
In the area of post press processing, in which printed materials which come from a printing press are processed further by means of gathering, folding, inserting, stapling or the like to form a finished printed product, a newspaper, brochure or the like, when high processing throughputs of, for example, several 10 000 products per hour are involved, use is made of specific transport devices like the known gripper transporters in order to be able to transport the large quantities of products which accumulate between various further processing stations in a short time.
Together with the associated transport devices, the various further processing stations form processing lines, on which the products are subjected to predefined processing steps. In order to increase the flexibility of the further processing, processing lines are increasingly being devised on which the products passing through can be fed as desired to different processing steps. For instance, it is possible, in a transport device having a closed circulation, to arrange for selected products to circulate repeatedly in order to feed them repeatedly to the same processing step (insertion or the like).
In order that such a flexible mode of operation can be carried out with the necessary freedom from error, it must be possible to track the location of the individual products within the transport device without ambiguity. If, for example in a gripper transporter, a product which is to be processed by a processing station is located in a specific gripper of the transporter, the processing station must know when this gripper is located in its area of access in order that it can make access to the correct gripper.
Beginning a specific length of the transport device or beginning at a specific number of grippers in the gripper transporter, an additional source of error with regard to tracking the position of the product within the transport device is introduced by the play between the individual mechanical elements in the transporter. The play between the individual elements adds up, so that when starting up and braking, the actual distances between the elements change. In the case of elements which, for example, are arranged far from one another in a chain, this effect—also called “jitter”—can lead to the situation in which the relative position of the elements can no longer be determined unambiguously. Even with a known position of individual elements, as a result of the “jitter” it is not possible to conclude accurately about the position of far-removed elements.
Furthermore, in the event of a breakdown in the transport device, it is important to be able to detect quickly and reliably after the plant has been started up again where the individual product or grippers are currently located, in order that the predefined processing program can be continued without error.
From WO 2008/043194 A2 it is known to provide flexible flat products, preferably printed products, which have been produced in a conventional high performance printing process, with an identification means in the form of an RFID tag, between the high performance printing device, and a first further processing device connected downstream of the printing device. In this case, the RFID tags do not need to be attached directly in or to the printed product; instead they can also be assigned detachably, temporarily physically directly, to the printed product. The identification means can in this case be formed, for example, in a transport unit assigned to the printed product for a specific period and a specific section of the transport path, for example a support of a ladder conveyor or a gripper of a gripper transporter. Such a temporary ability to identify a gripper remains product-based, however, and therefore does not create the ability to identify the transport means permanently and unambiguously overall.
From WO 2008/144945 A2 it is known to provide tags that can be read in and/or out without contact on the clamps of a gripper transporter, in order to read predefined quantities of data into and/or out of the tags of a gripper, to bring a read-in/read-out device into the vicinity of the respective gripper and to move it together with the respective gripper over a selected section of the transport path. In this way, despite the high linear speeds of the grippers during operation, it is possible not only to identify the gripper unambiguously but also to establish and to document its history, operating data and its partial or complete failure at any time. For instance, it is firstly possible to ensure that, during repair of the gripper following a failure, the correct replacement parts are installed. Furthermore, in the event of a fault, the gripper which has caused the breakdown can be identified immediately and, following a repair, the plant can be started up again where it has stopped. Finally, the individualization of the grippers can advantageously be used to control the plant if, for example, specific grippers with specific products are to be branched out (removed) from the advancing series of grippers and fed to separate processing operations. In this case, the identity of the grippers is checked continuously and the branching operation is initiated when the gripper sought has reached the branching point. In a corresponding way, the gripper branched off with the separately processed product can be introduced (input) into the product stream again later at a predetermined location. To this end, the tags that are used are preferably tags that can be read in and/or out by radio, in particular in the form of RFIDs. This type of individualization of the grippers by equipping each gripper with an individual feature in the form of a readable label is comparatively complicated, since here each individual gripper must be treated specifically.
EP 0 961 188 A1 indicates a method for controlling conveyance and processing of piece goods which is simple in terms of control engineering and less complicated in terms of apparatus, in such a way that it can be applied both to systems having conveyor chains of any desired length and also to systems having more or less mutually independent holding means (e.g. grippers of a gripper transporter), to be specific when an extremely wide range of stations are used at freely selectable points of the conveying path, for actions which relate to every object or holding means conveyed in or only to a specific selection of objects or holding means. In addition, when the method is used, the effort for commissioning, for a cold start, for statistical monitoring of the holding means condition and for maintenance work in which holding means are replaced is intended to be a minimum.
To this end, a plurality of holding means that can be moved on an intrinsically closed conveying path are equipped as signal generators. Each station has sensory means for generating a signal when a signal generator is conveyed through. Furthermore, the stations have a clock generator internal to the station or sensory means for detecting holding means conveyed in, and also a counter for counting the cycles of the clock generator or for counting the holding means conveyed through.
By means of a signal generated by a signal generator in a station, the counter in the station is reset and, if appropriate, a phase shift between station clock and conveying clock is registered or set to zero. Between each two signal generators, a number of holding means not equipped as signal generators are provided, the number being different for each pair of signal generators. By means of the number of holding means between a first signal generator arranged downstream in the flow and a second signal generator arranged upstream in the flow, which number is counted and registered as station cycles or sensor-registered holding means, the second signal generator can be identified unambiguously (signal generator identification). By means of the current counter reading and the signal generator identification of the preceding signal generator, each holding means which is currently being conveyed through a reference point of the station can be identified unambiguously. Important to the success of this method is the non-equal segmentation of the conveying path by means of the pairs of signal generators which, in pairs, must have a different spacing. However, maintaining these different spacings entails organisational effort.
DE 696 17 400 T2 discloses a method for identifying and finding a gripper during the transport of printed materials with the aid of a gripper conveyor, the gripper conveyor being subdivided into a number of gripper sections and the gripper sections being made sufficiently short to avoid disruptive length changes of the relevant sections during operation. The provision of a characteristic identification code for each section makes it possible for the section and the start of the said section to be identified. By allocating a characteristic identity to the gripper on the basis of the membership of the latter to its section and on the basis of its position in the latter, it is possible for the gripper to be found reliably by sensing the section code and the address of the gripper within its specific section. However, with this technique, simplified continuous numbering of the grippers or clamps over the entire conveying section is not possible.